With a recent trend of miniaturization and weight lightening of electronic devices, miniaturization and weight lightening of batteries used therein as a power supply have been also required. Secondary batteries are commercialized as batteries that are small, light, and chargeable and dischargeable with high capacity, and used in portable electronic devices such as small video cameras, mobile phones and laptops, communication devices and the like.
Secondary batteries are an energy storage system having high energy and power, and have excellent advantages of having higher capacity or operating voltage compared to other batteries. However, battery safety becomes a problem due to such high energy, and there is a risk of explosion or fire. Particularly, in hybrid vehicles and the like recently receiving an attention, high energy and output properties are required and accordingly, such safety is more important.
A secondary battery is generally formed with a positive electrode, a negative electrode and an electrolyte, and charge and discharge become possible since metal ions perform a role of transferring energy while travelling back and forth between both electrodes. Metal ions come out of a positive electrode active material by first charge, are inserted into a negative electrode active material, that is, carbon particles, and eliminated from carbon particles again during discharge.
Meanwhile, with the development of portable electronic devices, high capacity batteries have been continuously required, and researches on high capacity negative electrode materials having significantly higher capacity per unit weight compared to carbon used as an existing negative electrode material have been actively conducted.